The present invention relates in general to a power assist handle for generating control signals and, more specifically, to a power assist handle for diagnostic imaging equipment, such as a spot-film device.
Two-axis (i.e., four-way) power assist handles provide motion along two orthogonal axes and include a means of sensing the motion. A signal indicating the motion is generated by the sensors and provided to a power assist device, such as a servo system for moving the device to which the handle is attached.
Two-axis power assist handles are commonly used on the movable portions of medical diagnostic equipment, such as an X-ray spot-film device used in connection with radiographic and fluoroscopic systems. The desired directions of motion for these devices are up-down and left-right. These motions should be independently achieved within the handle itself, and motion along each axis should be independently sensed. Motion on each axis should be achievable simultaneously and by applying force at any location of the handle.
Previous handle designs have accomplished the necessary functions by placing two sensors on a rigid support and using a member which forms the hand grip and encloses the support to push against a load- or displacement-sensing part of the sensors. For example, moving core transformers have been employed where handle motion changes the coil coupling. The voltage on the secondary winding or windings can be sensed to indicate handle motion. However, due to the small size of these coils, high frequency primary voltage is required which leads to high-cost components. Furthermore, this type of mechanism introduces friction which creates hysteresis in the control motion. This type of mechanism cannot prevent rotation about all three axes. Consequently, motion of the handle is dependent on the location at which the displacement force is applied.
Accordingly, it is a principal object of the present invention to provide a power assist handle having motion in only two directions, with no rotation about any axis.
It is another object of the present invention to substantially eliminate friction in a power assist handle.
It is a further object of the invention to provide sensors for a power assist handle each sensitive only to motion in one direction.
It is yet another object of the invention to provide a power assist handle using low-cost d.c. electronics.
It is yet another object of the invention to provide a power assist handle wherein displacement of the handle is essentially linear with applied load and wherein the handle has negligible hysteresis.
It is still another object of the invention to provide handle motion which is substantially independent of the location on the handle where displacement force is applied.